TM 9-2320-280-34
1.
Negligible damage. Minor dents, nicks, scores, cracks, and holes in body panels which are
within or are brought within reasonable limits by a simple procedure, without extensive rework, are considered
negligible damage. These defects should be considered more serious if located in main structural members
such as body side rails, "A" pillars, or floor crossmembers rather than in body panels such as cowls or rear
wheelhouses. Deep wrinkles of undetermined origin in body panels should not be classed as negligible until the
source of wrinkles has been investigated and positively identified. Damage other than small dents, holes,
nicks, and scratches will require repair or replacement of the part. Refer to pars 22-8.f for repair of negligible
damage.
(a)
Negligible cracks. Isolated cracks less than 0.50 in. (1.27 cm) long may be classified
as negligible cracks provided they are stop drilled at each end to stop propagation.
(b)
Negligible holes. Isolated holes no more than 0.50 in. (1.27 cm) diameter, after they
are made round with smooth edges are classified as negligible holes, provided the distance from the edge of
the hole to the nearest line of rivets exceeds the diameter of the hole.
(c)
Negligible dents and distortion. Small dents and distorted areas may be classed as
negligible if they can be repaired by hammering or bending without causing the material to crack. Heat may
not be used for reforming.
2.
Damage repairable by patching. Damage beyond negligible must be repaired, or the section.
Replaced. Patches can often be applied over damaged body panels provided damaged area is first trimmed
to remove sharp edges or notches which could cause the start of new cracks. The patch must then be sized to
overlap the area to allow for attaching rivets. Refer to para. 22-8.g for repair by patching.
3.
Damage repairable by insertion. In certain cases, patch repairs may not be desirable because
of impracticality or because a flush surface is desired. In this case, damaged area must be cut away and a
partial replacement of equivalent material inserted flush with adjacent areas and backed up with a doubler.
Refer to para. 22-8.h for repair by insertion.
4.
Damage necessitating replacement of parts. Parts too badly damaged for repair, or where
replacement is easier than repair, fall into this category. Repair of welded assemblies such as body mounts are
also in this category. Welded assemblies cannot be re-welded without destroying strength of the part and must
be replaced.
c. Rivet Failure. Signs of rivet failure include tipped heads, looseness, and sometimes chipped or
cracked paint. If heads are tipped in the same direction and rivets are loose in consecutive groups, the joint
had undergone excessive load. Rivet heads which are tipped in different directions, and are not in groups may
be improperly installed. With chipped or cracked paint, it may be necessary to remove paint to check true
condition of rivets. Rivets subjected to critical loads but showing no distortion, should be inspected if failure is
suspected. The head should be drilled off, and the shank should be carefully punched out. Failure is indicated
by notched rivet shank and misaligned holes. Flush rivets showing head slippage within the dimple or
countersink indicate either sheet bearing or rivet shear failure and must be removed for inspection and
replacement. If failure of rivets cannot be detected by visual inspection, the joint can be checked by drilling
and punching out several rivets. If rivet shanks are notched, rivets should be replaced with next larger size
rivets. If rivet holes show elongation due to local failure in tearing of the sheet, next larger size rivet must be
used in replacement. Any deformation of the sheet around the rivet, tear outs, or cracks between rivets usually
indicates partially failed or damaged rivets. Complete repair of the joint will require replacement by next larger
size rivets. Use the next .031 in. (0.79 mm) larger diameter rivet to obtain a tight joint when original hole has
been enlarged. If original size rivet is installed, the rivet would not be able to carry its share of the shear load,
and the joint would not meet its strength requirements.
d. Lockbolt Failure. Lockbolts are used to withstand tension loads and high shear loads. These
fasteners are installed in their holes with an interference fit. No looseness can be permitted. Lockbolts showing
evidence of being stretched, broken, loose in their holes, or having heads that do not set flat against the
surface must be replaced. Guidelines used in 22-6.c for detecting rivet failures also apply to lockbolts.
22-6
